Re: [Qemu-devel] [PATCH v2] qmp: add query-cpus-fast

[Viktor Mihajlovski]

On 08.02.2018 21:33, Eduardo Habkost wrote:
> On Thu, Feb 08, 2018 at 11:17:32AM -0500, Luiz Capitulino wrote:
> [...]
>> The "halted" field is somewhat controversial. On the one hand,
>> it offers a convenient way to know if a guest CPU is idle or
>> running. On the other hand, it's a field that can change many
>> times a second. In fact, the halted state can change even
>> before query-cpus-fast has returned. This makes one wonder if
>> this field should be dropped all together. Having the "halted"
>> field as optional gives a better option for dropping it in
>> the future, since we can just stop returning it.
> 
> I'd just drop it, unless we find a use case where it's really
> useful.
> 
> Also, the code that sets/clears cpu->halted is target-specific,
> so I wouldn't be so sure that simply checking for
> !kvm_irqchip_in_kernel() is enough on all targets.
> 
Right, the present patch effectively disables halted anyway (including
s390). So it may be cleaner to just drop it right now.
Assuming the presence of architecure-specific data, libvirt can derive a
halted state (or an equivalent thereof) from query-cpus-fast returned
information.

-- 
Regards,
 Viktor Mihajlovski